1. Field of the Invention
The present invention generally relates to a fingerprint detection apparatus, and more particularly to a fingerprint detection apparatus including a light source for irradiating light to a finger and an image detecting part for detecting an image of a fingerprint for detecting a fingerprint based on a detection signal output from the image detecting part.
2. Description of the Related Art
Among various typical fingerprint detection apparatuses, there is, for example, one fingerprint detection apparatus that obtains images of fingerprints by activating a fingerprint detection apparatus using software that controls a system for reducing power consumption, and another fingerprint detection apparatus that obtains images of fingerprints by activating software upon detecting a finger contacting the fingerprint detection apparatus. From the aspect of operability and low power consumption, the latter may be chosen more often in a case of a battery operated system.
As for a detecting part for detecting a finger contacting an image pickup surface, an optical type fingerprint detection apparatus may have, for example, an electromagnetic detecting part that detects changes of resistance or capacitance. Alternatively, the optical type fingerprint detection apparatus may have an optical detecting part that is mounted outside of the fingerprint detection apparatus. However, such detecting parts exhibit difficulty in operating consistently due to, for example, the condition of a finger (moist finger, dry finger) or climate. Furthermore, since the resistance change detection type or the capacitance change detection type has an electrode provided to its finger-contact area, static electricity having greater energy than the electrode may be applied to the detection apparatus due to discharge of static electricity created from chemical fiber clothing of the user, thereby damaging the electronic circuits inside the detection apparatus.
In a case of using the optical type fingerprint detection apparatus having an optical detecting part mounted outside of the detection apparatus, the detecting part may be adversely affected by factors such as surrounding brightness or disturbance by sunlight. Such a type of apparatus is required to detect concavo/convexo parts of a fingerprint image obtained when contacting a finger under various atmospheric conditions (for example, see Japanese Laid-Open Patent Application No. 2005-202694).
Furthermore, such an optical type fingerprint detection apparatus is difficult to use for a battery-operated apparatus such as a mobile phone since its light source is required to be lit up when performing fingerprint detection.
Although it is possible to realize a fingerprint detecting function by modifying the configuration or the detection algorithm of the optical type fingerprint detection apparatus, additional components are often required for attaining a satisfactory fingerprint detecting function. This leads to increase of manufacturing cost of the apparatus. Furthermore, with the type that detects concavo/convexo parts of a fingerprint image, there are significant differences in reference values for determining detection of a fingerprint according to the atmospheric conditions (e.g., outdoors in daylight, nighttime).